French authorities have dropped all terrorism charges against Lebanese-Canadian professor Hassan Diab in the 1980 Paris synagogue bombing.

He was charged with first-degree murder in connection to the bombing that killed four people and injured 40.

He was arrested in Canada in 2008 and extradited to France in 2014. He spent three years in prison.

Mr Diab, 64, has always maintained his innocence and says he was in Lebanon at the time of the attack.

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“Canada welcomes the recent court decision to release Hassan Diab,” said Brittany Venhola-Fletcher, a spokeswoman for Canada’s department of international affairs.

Ms Venhola-Fletcher was not able to say when the former University of Ottawa professor would be returning to Canada.

French judges ruled the evidence “was not convincing enough” and ordered Mr Diab to be released on Friday. His extradition to France has triggered a number of people to call for an update to Canada’s extradition act.

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French prosecutors say they will appeal the decision.